John Y. Brown Jr., Kentucky's jet-set governor, and his wife, television sportscaster Phyllis George, have thrown Kentucky politics into another tizzy.

After insisting for months that they didn't want to be kingmakers, the flamboyant couple abruptly changed their minds, and plunged into the Kentucky gubernatorial race in the final week of what had been a lackluster campaign.

They did it with the same kind of unpredictable pizazz that has characterized their whirlwind political life.

Brown, who had been in Los Angeles working on a national Democratic telethon scheduled for this week, unexpectedly flew back to the state on May 16 and endorsed Dr. Grady Stumbo, who had been running a weak third in a three-way race for the Democratic nomination.

"I couldn't stand by and see my state not have the very best," Brown said as the theme music from "Chariots of Fire" played in the background.

That night his wife began taping 30-minute television talk shows with Stumbo that were modeled after a series of similar shows that helped elect Brown, who is prohibited by law from seeking a second four-year term.

"Phyllis is going to do for Grady what she did for me," said Brown, who made a fortune during the years he owned Kentucky Fried Chicken. "In all honesty, I don't think I could have gotten elected without Phyllis, and in all honesty, I don't think Grady could get elected without Phyllis."

Stumbo's two opponents, Louisville Mayor Harvey Sloane and Lt. Gov. Martha Layne Collins, disagree with that assessment.

But there is little doubt that Brown's 11th-hour endorsement dramatically changed the dynamics of todays' Democratic primary. Political observers say that the race is too close to call and that each of the candidates has a chance of winning.

State Sen. Jim Bunning, a former major league pitching star, has only token opposition in the Republican gubernatorial primary, and is expected to win easily.

Sloane filmed a television commercial condemning Brown's endorsement of Stumbo, and said that Brown has become the major issue in the race.

"By trying to pick his own successor and ram his choice through the primary, he has turned Grady into nothing but a puppet," he said. "It isn't Grady Stumbo running at all. It's John Y. Brown."

Sloane, seeking to become the first mayor of Louisville to be elected governor, had been running even with Collins, who is attempting to become the state's first female governor.

Sloane, 47, is a physician who moved to Kentucky in the 1960s to work with the poor in the mountainous eastern part of the state and later in the Louisville slums. In 1979, he ran for governor with the support of labor, blacks and liberals, who had helped elect him mayor, and lost to Brown.

But this year Sloane has courted business and right-to-life groups. He has also alienated organized labor by refusing to say that he would veto right-to-work legislation.

Some say that Sloane has lost his idealism.

"He deceived Louisville. He deceived blacks. He used us for his political purposes and then dropped us," charged state Sen. Georgia Davis Powers, a prominent Louisville black leader. "We know it was for political expediency. When you're an advocate of black people, poor people and women you don't get a lot of campaign contributions."

"I don't think I've changed. I know my basic values haven't," Sloane said in an interview. "But times have changed and priorities have changed. We're in a time of basic economic survival. It's a fact of life that our state and the city of Louisville are having real economic difficulties."

Collins, 46, is a former school teacher with an All-America background. She grew up in a tiny central Kentucky town and was graduated from the University of Kentucky, where she was president of her sorority and a beauty queen.

She has raised more money ($2.2 million) and has more support in county courthouses than either of her opponents. Though she says she supports the Equal Rights Amendment, she has never taken a leadership role on any women's issue in the state and has little support from feminists.

At 38, Stumbo, a coal miner's son, is the youngest and most colorful candidate in the race. He is a physician and founded a well-publicized health clinic in the poverty-stricken hills of eastern Kentucky. He served as Brown's secretary of human resources.

Though he had attracted widespread support from organized labor, Stumbo lagged well behind Collins and Sloane in polls and fund-raising until Brown threw him his support. Suddenly, tens of thousands of dollars appeared to finance a final television blitz.